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V. T. Dolgopolov

Publications and source records attributed to V. T. Dolgopolov.

At least 55 records · Page 3Linked to original sources
arXiv2004

Charge redistribution between cyclotron-resolved edge states at high imbalance

We use a quasi-Corbino sample geometry with independent contacts to different edge states in the quantum Hall effect regime to investigate a charge redistribution between cyclotron-split edge states at high imbalance. We also modify Buttiker formalism by introducing local transport characteristics in it and use this modified Buttiker picture to describe the experimental results. We find that charge transfer between cyclotron-split edge states at high imbalance can be described by a single parameter, which is a transferred between edge states portion of the available for transfer part of the electrochemical potential imbalance. This parameter is found to be independent of the particular sample characteristics, describing fundamental properties of the inter-edge-state scattering. From the experiment we obtain it in the dependence on the voltage imbalance between edge states and propose a qualitative explanation to the experimental findings.

cond-mat.mes-hall↗
arXiv2004

Manifestation of the bulk phase transition in the edge energy spectrum in a two dimensional bilayer electron system

We use a quasi-Corbino sample geometry with independent contacts to different edge states in the quantum Hall effect regime to investigate the edge energy spectrum of a bilayer electron system at total filling factor $ν=2$. By analyzing non-linear $I-V$ curves in normal and tilted magnetic fields we conclude that the edge energy spectrum is in a close connection with the bulk one. At the bulk phase transition spin-singlet - canted antiferromagnetic phase $I-V$ curve becomes to be linear, indicating the disappearance or strong narrowing of the $ν=1$ incompressible strip at the edge of the sample.

cond-mat.mes-hall↗
arXiv2004

Quantum phase transitions in two-dimensional systems

Experimental data on quantum phase transitions in two-dimensional systems (superconductor-insulator, metal-insulator, and transitions under conditions of integer quantum Hall effect) are critically analyzed.

cond-mat.mes-hall↗
arXiv2003

Remote-doping scattering and the local field corrections in the 2D electron system in a modulation-doped Si/SiGe quantum well

The small, about 30% magnetoresistance at the onset of full spin polarization in the 2D electron system in a modulation-doped Si/SiGe quantum well gives evidence that it is the remote doping that determines the transport scattering time. Measurements of the mobility in this strongly-interacting electron system with remote-doping scattering allow us to arrive at a conclusion that the Hubbard form underestimates the local field corrections by about a factor of 2.

cond-mat.str-el↗
arXiv2003

Observation of two relaxation mechanisms in transport between spin split edge states at high imbalance

Using a quasi-Corbino geometry to directly study electron transport between spin-split edge states, we find a pronounced hysteresis in the I-V curves, originating from slow relaxation processes. We attribute this long-time relaxation to the formation of a dynamic nuclear polarization near the sample edge. The determined characteristic relaxation times are 25 s and 200 s which points to the presence of two different relaxation mechanisms. The two time constants are ascribed to the formation of a local nuclear polarization due to flip-flop processes and the diffusion of nuclear spins.

cond-mat.mes-hall↗
arXiv2003

Sharply increasing effective mass: a precursor of the spontaneous spin polarization in a dilute two-dimensional electron system

We have measured the effective mass, m, and Lande g-factor in very dilute two-dimensional electron systems in silicon. Two independent methods have been used: (i) measurements of the magnetic field required to fully polarize the electrons' spins and (ii) analysis of the Shubnikov-de Haas oscillations. We have observed a sharp increase of the effective mass with decreasing electron density while the g-factor remains nearly constant and close to its value in bulk silicon. The corresponding strong rise of the spin susceptibility may be a precursor of a spontaneous spin polarization; unlike in the Stoner scenario, it originates from the enhancement of the effective mass rather than the increase of g-factor. Furthermore, using tilted magnetic fields, we have found that the enhanced effective mass is independent of the degree of spin polarization and, therefore, its increase is not related to spin exchange effects, in contradiction with existing theories. Our results show that the dilute 2D electron system in silicon behaves well beyond a weakly interacting Fermi liquid.

cond-mat.str-el↗
arXiv2003

Direct measurements of the spin and the cyclotron gaps in a 2D electron system in silicon

Using magnetocapacitance data in tilted magnetic fields, we directly determine the chemical potential jump in a strongly correlated two-dimensional electron system in silicon when the filling factor traverses the spin and the cyclotron gaps. The data yield an effective g-factor that is close to its value in bulk silicon and does not depend on filling factor. The cyclotron splitting corresponds to the effective mass that is strongly enhanced at low electron densities.

cond-mat.str-el↗
arXiv2003

Spin-independent origin of the strongly enhanced effective mass in a dilute 2D electron system

We have accurately measured the effective mass in a dilute two-dimensional electron system in silicon by analyzing temperature dependence of the Shubnikov-de Haas oscillations in the low-temperature limit. A sharp increase of the effective mass with decreasing electron density has been observed. Using tilted magnetic fields, we have found that the enhanced effective mass is independent of the degree of spin polarization, which points to a spin-independent origin of the mass enhancement and is in contradiction with existing theories.

cond-mat.str-el↗
arXiv2002

Strong enhancement of the valley splitting in a 2D electron system in silicon

Using magnetocapacitance data, we directly determine the chemical potential jump in a strongly correlated 2D electron system in silicon when the filling factor traverses the valley gap at ν=1 and ν=3. The data yield a valley gap that is strongly enhanced compared to the single-particle value and increases LINEARLY with magnetic field. This result has not been explained by existing theories.

cond-mat↗
arXiv2002

On Effective Electron Mass of Silicon MOSFET at Low Electron Density

The trial wave function method developed in Ref.s \cite{gutz,brink} for the case of narrow {\it s}-band in a perfect crystal is adapted for calculation of the density dependence of the effective mass and the Lande factor in a dilute two-dimensional electron system. We find that the effective mass has a tendency to diverge at a certain critical concentration, whereas the $g$ factor remains finite.

cond-mat.mes-hall↗
arXiv2002

Comment on "Low-Density Spin Susceptibility and Effective Mass of Mobile Electrons in Si Inversion Layers"

In a recent Letter (PRL 88, 196404 (2002)), the effective g-factor and the effective mass have been studied by Pudalov et al. in a dilute 2D electron system in silicon. The authors contrast their data with the data obtained by our group (Shashkin et al., PRL 87, 086801 (2001)) and claim that the spin susceptibility "increases gradually with decreasing density", which "does not support the occurrence of spontaneous spin polarization and divergence of gm..." The purpose of this Comment is to show that all available experimental data, including those of Pudalov et al., are consistent with each other and are in favor of a spontaneous spin polarization and divergence of gm at a finite electron density in this 2D system.

cond-mat.str-el↗
arXiv2001

Shifting the quantum Hall plateau level in a double layer electron system

We study the plateaux of the integer quantum Hall resistance in a bilayer electron system in tilted magnetic fields. In a narrow range of tilt angles and at certain magnetic fields, the plateau level deviates appreciably from the quantized value with no dissipative transport emerging. A qualitative account of the effect is given in terms of decoupling of the edge states corresponding to different electron layers/Landau levels.

cond-mat.mes-hall↗
arXiv2001

Sharp increase of the effective mass near the critical density in a metallic 2D electron system

We find that at intermediate temperatures, the metallic temperature dependence of the conductivity σ(T) of 2D electrons in silicon is described well by a recent interaction-based theory of Zala et al. (Phys. Rev. B 64, 214204 (2001)). The tendency of the slope dσ/dT to diverge near the critical electron density is in agreement with the previously suggested ferromagnetic instability in this electron system. Unexpectedly, it is found to originate from the sharp enhancement of the effective mass, while the effective Lande g factor remains nearly constant and close to its value in bulk silicon.

cond-mat.str-el↗
arXiv2001

Separately contacted edge states: A new spectroscopic tool for the investigation of the quantum Hall effect

Using an innovative combination of a quasi-Corbino sample geometry and the cross-gate technique, we have developed a method that enables us to separately contact single edge channels in the quantum Hall regime and investigate equilibration among them. Performing 4-point resistance measurements, we directly obtain information on the energetic and geometric structure of the edge region and the equilibration-length for current transport across the Landau- as well as the spin-gap. Based on an almost free choice in the number of participating edge channels and their interaction-length a systematic investigation of the parameter-space becomes possible.

cond-mat.mes-hall↗
arXiv2001

Indication of the ferromagnetic instability in a dilute two-dimensional electron system

The magnetic field B_c, in which the electrons become fully spin-polarized, is found to be proportional to the deviation of the electron density from the zero-field metal-insulator transition in a two-dimensional electron system in silicon. The tendency of B_c to vanish at a finite electron density suggests a ferromagnetic instability in this strongly correlated electron system.

cond-mat.str-el↗
arXiv2001

Quantization of the Hall conductivity well beyond the adiabatic limit in pulsed magnetic fields

We measure the Hall conductivity, $σ_{xy}$, on a Corbino geometry sample of a high-mobility AlGaAs/GaAs heterostructure in a pulsed magnetic field. At a bath temperature about 80 mK, we observe well expressed plateaux in $σ_{xy}$ at integer filling factors. In the pulsed magnetic field, the Laughlin condition of the phase coherence of the electron wave functions is strongly violated and, hence, is not crucial for $σ_{xy}$ quantization.

cond-mat.mes-hall↗
arXiv2000

Response of the two-dimensional electron gas of AlGaAs/GaAs heterostructures to parallel magnetic field

We study the transport properties of the two-dimensional electron gas in AlGaAs/GaAs heterostructures in parallel to the interface magnetic fields at low temperatures. The magnetoresistance in the metallic phase is found to be positive and weakly anisotropic with respect to the orientation of the in-plane magnetic field and the current through the sample. At low electron densities ($n_s< 5\times 10^{10}$ cm$^{-2}$) the experimental data can be described adequately within spin-related approach while at high $n_s$ the magnetoresistance mechanism changes as inferred from $n_s$-independence of the normalized magnetoresistance.

cond-mat.mes-hall↗